1. Field of the Invention
The present invention relates to an apparatus and a method for generating a terahertz (THz) wave, and more particularly, to an apparatus and a method for generating a THz wave by heterodyning optical wave and electrical wave.
2. Description of the Related Technology
Terahertz (THz) waves can be generated by photo-mixing using a fiber optic probe (FOP) and an objective lens. The photo-mixing is performed by injecting the coupled laser beams into a high-speed and high-frequency semiconductor device through an optical lens or a single-mode optical fiber, and generating and detecting microwave and THz waves. However, in this case, because the diameter of the laser beam is much larger than semiconductor devices, degradation of the stability of a detected signal and the high noise figure arises from lack of the device accessibility and scanning performance of FOP.
THz waves can also be generated by heterodyning two optical waves. The heterodyning of the two optical waves is performed by injecting optical beams with frequencies ω1 and ω2 come from two lasers into a near-field fiber optic probe (NFOP) using an optical coupler. Then, through the interaction between a high-speed and high-frequency device and an optical wave of a frequency ωb (=ω1˜ω2) come from a probe tip (end) with a diameter of less than 0.1 μm, a millimeter wave with a frequency (ωb/2π) corresponding to the above-described frequency difference (ω1˜ω2) is generated and detected. Thereby, from this method, the resolution and noise figure of the mixed light are improved.
However, it is found that using the high-speed and high-frequency InP-based hetero-junction bipolar transistor (HBT), whenever high frequency characteristics are measured under 1 THz, the practical characteristics are considerably different from the simulated results. Therefore, the heterodyne method of two optical waves has limitations to evaluate characteristics of high-speed and high-frequency devices in a range from 0.1 to 10 THz.